The present invention relates to a mixer for crushing cement balls contained in cement paste to homoginize the cement paste and a method of producing high-strength or ultra-high strength concrete or mortar by use of the mixer.
Heretofore, as a technique for kneading concrete, as shown in FIG. 14, a so-called batch kneading method has been widely used in which water, cement, fine aggregate, coarse aggregate, pozzolan and admixtures are put in a mixer at a time and kneaded together. In order to produce high-strength, high-quality concrete, a double-mixing method as shown in FIG. 15 is also used these days. In this method, only cement paste or mortar is kneaded in a mixer and then fine aggregate and coarse aggregate are added to the cement paste and kneaded together to produce concrete. Mixers used for producing concrete in these methods include gravity type mixers, horizontal pan type forced action mixers, twin-shaft mixers, continuous kneading mixers, omni-mixers, etc.
But, cement to be treated with the batch kneading process has a fine particle size (approx. 5500 cm.sup.2 /g in specific surface area). Thus, very hard cement balls are formed by a large cohesive force produced when the cement contacts water. It is difficult to crush such cement balls even if the cement is kneaded together with fine aggregate and coarse aggregate with a conventional mixer as described above. This hampers the production of concrete made of uniform cement paste. Concrete using a pozzolan material having a super-fine particle size (about 20 m.sup.2 /g in specific surface area) such as silica fume shows a particularly strong cohesive force between the pozzolan material and water. Thus, the above-described mixers can hardly crush the cement balls made of this material.
There is a growing tendency these days to use super-high-strength materials (1000 kg f/cm.sup.2 at the age of 28 days) as concrete for super-high-rise building structures. Since such concrete uses, in addition to a super-fine pozzolan material, a high-performance water reducing agent or a high superplasticizer in order to reduce the ratio of a water binding agent, its viscosity is extremely high. Thus, it is virtually impossible with the conventional batch mixing method shown in FIG. 14 to crush cement balls even if a powerful forced action mixer is used. Thus it is impossible to produce high-quality, high-strength or super-high strength concrete.
With the double mixing method shown in FIG. 15, since a conventional mixer as described above is used to knead cement paste or mortar, the crushing of the cement balls difficult. Thus, high-quality, high-strength concerete is difficult to obtain.